1. Field of the Invention
The present invention relates generally to a liquid crystal display using a liquid crystal having a spontaneous polarization, and a method for producing the same.
2. Description of Related Art
Liquid crystal displays have characteristics, such as low electric power consumption, light weight and thin type, and are widely used as monitors for personal computers and car navigation systems. However, as compared with CRTs, there are disadvantages in that the speed of response is slow, the viewing angle is narrow, and so forth. With the scale up and the higher resolution of liquid crystal displays, the requirements for a fast response and a wide angle of visibility are enhanced.
Liquid crystal displays using spontaneous polarization are widely noticed as a display mode capable of realizing a fast response. The spontaneous polarization is inherent in a liquid crystal, or induced by applying an electric field to the liquid crystal. Examples of such liquid crystal materials (display modes) include surface stabilized ferroelectric liquid crystal (SS-FLC), monostable ferroelectric liquid crystal, deformed helix ferroelectric liquid crystal (DHF), twisted ferroelectric liquid crystal (twisted FLC), alternating polarization domain (APD), polymer stabilized ferroelectric liquid crystal, anti-ferroelectric liquid crystal (including thresholdless anti-ferroelectric liquid crystal), and electro-clinic effect.
In order to realize full-color displays by combining the above described display modes with active elements, it is desired that the switching of liquid crystal molecules does not produce domains. In International Conference on Ferroelectric Liquid Crystal (FLC 99) which was open in Germany on August 1999, the continuous director rotation (CDR) mode was reported. In this mode, it is possible to carry out a full-color half-tone display since the optical axes (long axes) of liquid crystal molecules continuously rotate in accordance with applied voltages.
In the CDR mode, a smectic phase is formed by applying a monopolar electric field (dc electric field) between pixel electrodes and a counter electrode during the phase transition of the liquid crystal material from the nematic phase or the isotropic phase to the chiral smectic C phase. At this time, although a desired monopolar electric field can be applied to a region in which the pixel electrodes face the counter electrode, a desired electric field can not be applied to a region outside of the pixel electrodes. Therefore, a uniform liquid crystal can not be obtained outside of the pixel region. After the inventors diligently studied, it was found that the following problem is caused because of ununiform alignment outside of the pixel region.
That is, if the liquid crystal is driven at room temperatures for 1000 hours or more or at a temperature of 10xc2x0 C. or lower for 50 hours or more, the turbulence of alignment around the pixel region is propagated into pixels, so that light leakage occurs to lower contrast.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a liquid crystal display which can prevent light from leaking out from the peripheral portion of pixels and which has a high display performance, and a method for producing the same.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a liquid crystal display comprises: an array substrate including a plurality of scanning lines and a plurality of signal lines, the scanning lines and the signal lines being formed on a first substrate in the form of a matrix, a plurality of switching elements which are formed at points of intersection between the scanning lines and the signal lines ,one end of each of the switching elements being connected to a corresponding one of the signal lines, and each of the switching elements carrying out a switching action in response to a signal of a corresponding one of the scanning lines, a plurality of pixel electrodes, each of which is connected to the other end of a corresponding one of the switching elements, and a first alignment layer which is formed on the first substrate so as to cover the pixel electrodes; a counter substrate including a counter electrode which is formed on a second substrate, and a second alignment layer which is formed on the second substrate so as to cover the counter electrode; and a light control layer sandwiched between said array substrate and said counter substrate, and including a liquid crystal material having a spontaneous polarization and having a nematic phase or an isotropic phase on a high-temperature side of a chiral smectic C phase, an optical axis of liquid crystal molecules in said light control layer substantially staying when no electric field or a first electric field of a first polarity are applied to said liquid crystal material, and said optical axis of said liquid crystal molecules responding in accordance with a magnitude of a second electric field of a second polarity different from said first polarity when said second electric field is applied to said liquid crystal material, wherein an electric field between said scanning lines and said counter electrode has said first polarity when said switching elements turn on.
The switching elements may be disposed under said pixels.
A direction of a smectic layer in the light control layer preferably has a distribution of 10xc2x0 or less.
If each of the switching elements has a negative TFT and if a smectic layer is formed by cooling the cell without the application of voltage, the first alignment layer has an alignment characteristic that the spontaneous polarization of liquid crystal molecules is directed to the first substrate when no voltage is applied to said liquid crystal material.
If each of the switching elements has a positive TFT and if a smectic layer is formed by cooling the cell without the application of voltage, the first alignment layer has an alignment characteristic that the spontaneous polarization of liquid crystal molecules is directed to the second substrate when no voltage is applied to said liquid crystal material.
According to another aspect of the present invention, there is provided a method for producing a liquid crystal display comprising an array substrate including a plurality of scanning lines and a plurality of signal lines, the scanning lines and the signal lines being formed on a first substrate in the form of a matrix, a plurality of switching elements which are formed at points of intersection between the scanning lines and the signal lines, one end of each of the switching elements being connected to a corresponding one of the signal lines, and each of the switching elements carrying out a switching action in response to a signal of a corresponding one of the scanning lines, a plurality of pixel electrodes, each of which is connected to the other end of a corresponding one of the switching elements, and a first alignment layer which is formed on the first substrate so as to cover the pixel electrodes; a counter substrate including a counter electrode which is formed on a second substrate, and a second alignment layer which is formed on the second substrate so as to cover the counter electrode; and a light control layer which is sandwiched between the array substrate and the counter substrate and which is made of a liquid crystal material having a spontaneous polarization and having a nematic phase or an isotropic phase on a high-temperature side of a chiral smectic C phase, the method comprising: forming a chiral smectic C phase with applying an electric field of a polarity between the pixel electrodes and the counter electrode when a phase transition of the liquid crystal material from a nematic phase or an isotropic phase to the chiral smectic C phase occurs, wherein said polarity of said electric field equals to a polarity of an electric field between the counter electrode and the scanning lines when the switching elements turn on.